The initiative in the organization of the conference was taken by the President of Commission 33 of the International Astronomical Union and financial aid was received from U.N.E.S.C.O. At the invitation of Dr P. J. van Rhijn, Director of the Kapteyn Astronomical Laboratory, Groningen, the meeting was held in the estate ‘Vosbergen’ near the city of Groningen and owned by the University of Groningen. The organizing committee consisted of J. H. Oort (Chairman), W. Baade, B. J. Bok, Ch. Fehrenbach, B. Lindblad, W. W. Morgan, P. P. Parenago, and A. Blaauw (Secretary), all of whom attended the conference. The other participants, who were invited either because they represented institutions which might take part in future galactic research, or because of the character of their research, were V. A. Ambartsumian, W. Becker, P. Couderc (representing the Commission for the Carte du Ciel), G. Haro, O. Heckmann, H. Spencer Jones, B. V. Kukarkin, J. J. Nassau, P. Th. Oosterhoff, L. Plaut (local Secretary), J. M. Ramberg, C. Schalen, J. Schilt, R. H. Stoy, B. Strömgren, P. J. van Rhijn. V. Kourganoff, P. G. Kulikovsky and O. A. Melnikov were present as interpreters.

The objects from which the structure and the kinematical properties of the nuclear region and the halo can be derived are in general those classified as population II objects: the RR Lyrae variables, population II Cepheids, RV Tauri variables, long-period variables with periods near 200 days, novae, planetary nebulae, bright red giants as found in globular clusters, and the blue stars found near the galactic poles which are probably similar to those found in globular clusters.

The population of the disk consists of a great variety of objects with a wide range of concentration towards the galactic plane and of peculiar motions. The extreme population I objects like interstellar gas and dust and super-giant stars, show quite different properties with respect to space distribution and motions, compared to such stars as, for instance, the common G and K giants. The discussions at the conference have concentrated on the observational possibilities of studying the correlation—or the lack of correlation—between the space distributions of different kinds of objects. From recent theoretical as well as observational work it has become apparent that there is a wide range in the ages of the stars contributing to the disk population, from a few million so some 1000 million years. The differences in the distributions of the various kinds of stars very probably must be interpreted in terms of these differences in age and evolution. The most intriguing problem for the present thus seems to be this: Can we trace large-scale structure in the distribution of objects of different ages, and can we derive information on the evolution of the galactic system and of the stars themselves from the degree of resemblance in the large-scale structure exhibited by different objects?

Numerous extensive studies of the space distribution of stars of different spectral types, based on star counts and colour measures, have in the past been published for different sections of the Milky Way.1 These studies have given information on the nearby obscuring clouds, and they have revealed marked differences between the distribution of different kinds of stars. They have not, however, given us the much desired insight into the large-scale features of the density distribution.

The potential possibilities of research in Kapteyn's Selected Areas at intermediate and high latitudes, where magnitudes and proper motions are already available, could be fully exploited if a more accurate spectral and luminosity classification would become available, especially for the later type stars. The purpose of work on faint stars in these latitudes is manifold. At the highest latitudes the improved data can serve for a new determination of the density distribution and of the force perpendicular to the galactic plane as a function of the distance z to the plane, K(z). The limiting magnitude may be set here at m = 13.0 (photographic). At intermediate latitudes one would hope to find the correlation between the density at some distance above the galactic plane with the density in the plane. Here the limit should be set at 13.5 or 14.0, so that G and K giants can be reached up to distances of 2 to 3 kparsecs from the Sun.

One of the most important fields for co-ordination in galactic research is the organization of programmes for proper motions and radial velocities. The need for accurate and more extensive data on stellar motions is strongly felt in connexion with the studies of the structure of the Galaxy and of the relation between the physical and the kinematical characteristics of the stars. Not long ago it seemed that meridian astronomy and photographic astrometry were rather remote from the main problems in astrophysics. It is realized now, that the study of stellar motions gives highly important information on the evolution of the stars and of the stellar system. A detailed account of the needs in this field, as discussed at the conference, follows:

1. (1) propermotions: photographicastrometryoffaintstars

A special session of the conference was devoted to discussion of work on associations. This subject of growing interest has many aspects; some of these have been dealt with already in the preceding sections.